The control of the α-Al2O3 polymorph in industrial scale was achieved in the beginning of the 1990's with commercial products based on U.S. Pat. No. 5,137,774. Later modifications of this patent have been used to deposit α-Al2O3 with preferred textures. In U.S. Pat. No. 5,654,035 an alumina layer textured in the (012) direction, in U.S. Pat. No. 5,766,782 in the (104)-direction and in U.S. Pat. No. 5,980,988 in the (110) direction are disclosed. In U.S. Pat. No. 5,863,640 a preferred growth either along (012), or (104) or (110) is disclosed. U.S. Pat. No. 6,333,103 describes a modified method to control the nucleation and growth of α-Al2O3 along the (10(10)) direction. U.S. Pat. No. 7,011,867 describes a method to obtain a strong (300) texture in α-Al2O3 using a texture modifying agent (ZrCl4). The prior-art processes discussed above use all high deposition temperatures of about 1000° C. U.S. Pat. No. 7,094,447 describes a technique to achieve a pronounced (102) texture. Enhanced deposition techniques to produce pronounced (104) and (116) textures are disclosed in US 2006/0199026 and US 2006/0141271, respectively.
Methods to produce a tough binder phase enriched zone in the upper part of a cemented carbide insert prior to coating are commonly referred to as gradient sintering. There are two types of processes, which are used to produce the binder phase enriched zone:    (i) By dissolution of the cubic phase near the surface (N-gradient). U.S. Pat. Nos. 4,277,283, 4,610,931, 4,830,930 and 5,106,674.    (ii) By controlled cooling or decarburisation (C-gradient) U.S. Pat. No. 5,106,674 and U.S. Pat. No. 4,830,930
The present invention is directed to these and other important needs, including an improved α-Al2O3 coated cutting tool insert.